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about_Methods

Updated: May 8, 2014

Applies To: Windows PowerShell 2.0, Windows PowerShell 3.0, Windows PowerShell 4.0

TOPIC
    about_methods

SHORT DESCRIPTION
    Describes how to use methods to perform actions on objects in Windows 
    PowerShell.
 

LONG DESCRIPTION
    Windows PowerShell uses objects to represent the items in data stores or
    the state of the computer. For example, FileInfo objects represent the
    files in file system drives and ProcessInfo objects represent the 
    processes on the computer.

    Objects have properties, which store data about the object, and methods
    that let you change the object.

    A "method" is a set of instructions that specify an action you can perform
    on the object. For example, the FileInfo object includes the CopyTo method
    that copies the file that the FileInfo object represents.

    To get the methods of any object, use the Get-Member cmdlet. Use its 
    MemberType property with a value of "Method". The following command
    gets the methods of process objects.

        PS C:\>Get-Process | Get-Member -MemberType Method
       
           TypeName: System.Diagnostics.Process

         Name                      MemberType Definition
         ----                      ---------- ----------
         BeginErrorReadLine        Method     System.Void BeginErrorReadLine()
         BeginOutputReadLine       Method     System.Void BeginOutputReadLine()
         ...
         Kill                      Method     System.Void Kill()
         Refresh                   Method     System.Void Refresh()
         Start                     Method     bool Start()
         ToString                  Method     string ToString()
         WaitForExit               Method     bool WaitForExit(int milliseconds), System.Void WaitForExit()
         WaitForInputIdle          Method     bool WaitForInputIdle(int milliseconds), bool WaitForInputIdle()


    To perform or "invoke" a method of an object, type a dot (.), the method
    name, and a set of parentheses "()". If the method has arguments, place the 
    argument values inside the parentheses. The parentheses are required 
    for every method call, even when there are no arguments.

    For example, the following command invokes the Kill method of processes
    to end the Notepad process on the computer. As a result, the instance
    of Notepad closes. (The Get-Process command is enclosed in parentheses 
    to insure that it runs before the Kill method is invoked.

        (Get-Process Notepad).Kill()

    Another very useful process is the Split method of strings. The 
    split method takes a delimiter character argument that tells the
    method where to split the string.

        PS C:\>$a = "Try-Catch-Finally"
        PS C:\>$a.Split("-")
        Try
        Catch
        Finally

    As shown in the previous examples, you can invoke a method on an
    object that you get by using a command or an object in a variable.

    Starting in Windows PowerShell 4.0, method invocation by using
    dynamic method names is supported.


 LEARNING ABOUT METHODS
    To find definitions of the methods of an object, go to help topic for
    for the object type in MSDN and look for its methods page. For example,
    the following page describes the methods of process objects 
   (System.Diagnostics.Process).

         http://msdn.microsoft.com/en-us/library/system.diagnostics.process_methods

    To determine the arguments of a method, review the method definition,
    which is like the syntax diagram of a Windows PowerShell cmdlet.

    A method definition might have one or more method signatures, which are
    like the parameter sets of Windows PowerShell cmdlets. The signatures 
    show all of the valid formats of commands to invoke the method.   
    
    For example, the CopyTo method of the 
    FileInfo class contains the following two method signatures:

        1. CopyTo(String destFileName)
        2. CopyTo(String destFileName, Boolean overwrite)

    The first method signature takes the destination file name (and
    a path). The following example use The first CopyTo method to copy 
    the Final.txt file to the C:\Bin directory.

        (Get-ChildItem c:\final.txt).CopyTo("c:\bin\final.txt")

    The second method signature take a destination file name and a 
    Boolean value that determines whether the destination file should
    be overwritten, if it already exists. 
 
    The following example use The second CopyTo method to copy 
    the Final.txt file to the C:\Bin directory, and to overwrite
    existing files.

        (Get-ChildItem c:\final.txt).CopyTo("c:\bin\final.txt", $true)

 METHODS OF SCALAR OBJECTS AND COLLECTIONS
    The methods of one ("scalar") object of a particular type
    are often different from the methods of a collection of objects 
    of the same type.

    For example, every process has a Kill method, but a collection 
    of processes does not have a Kill method. 

    Beginning in Windows PowerShell 3.0, Windows PowerShell tries
    to prevent scripting errors that result from the differing
    methods of scalar objects and collections.

    Beginning in Windows PowerShell 4.0, collection filtering by using
    a method syntax is supported.

    If you submit a collection, but request a method that exists 
    only on single ("scalar") objects, Windows invokes the method
    on every object in the collection.

    If the method exists on the individual objects and on the 
    collection, Windows PowerShell does not alter the result.

    This feature also works on properties of scalar objects and 
    collections. For more information, see about_Properties.


 EXAMPLES
    The following example runs the Kill method of individual
    process objects on a collection of process objects. This     
    example works only on Windows PowerShell 3.0 and later
    versions of Windows PowerShell.

    The first command starts three instances of the Notepad 
    process. The second command uses the Get-Process command
    to get all three instance of the Notepad process and save
    them in the $p variable. 

        PS C:\>Notepad; Notepad; Notepad
        PS C:\>$p = Get-Process Notepad
        
    The third command uses the Count property of all
    collections to verify that there are three processes
    in the $p variable.

        PS C:\>$p.Count
        3

    The fourth command runs the Kill method on all 
    three processes in the $p variable. 

    This command works even though a collection 
    of processes does not have a Kill method.

        PS C:\>$p.Kill()

    The fifth command uses the Get-Process command
    to confirm that the Kill command worked.

        PS C:\>Get-Process Notepad
        Get-Process : Cannot find a process with the name "notepad". Verify the process name and call the cmdlet again.
        At line:1 char:12
        + get-process <<<<  notepad
            + CategoryInfo          : ObjectNotFound: (notepad:String) [Get-Process], ProcessCommandException
            + FullyQualifiedErrorId : NoProcessFoundForGivenName,Microsoft.PowerShell.Commands.GetProcessCommand


     To perform the same task on Windows PowerShell 2.0,
     use the Foreach-Object cmdlet to run the method
     on each object in the collection.

        PS C:\>$p | Foreach-Object {$_.Kill()}

SEE ALSO
    about_Objects
    about_Properties
    Get-Member



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